This invention relates to devices for handling heavy components within a nuclear reactor, and in particular for removing and reinserting reactor internals and control rods during refueling.
Commercial nuclear power reactors have a plurality of fuel assemblies containing fissile fuel material wherein heat is generated and transferred to the working fluid. In a typical reactor, many of the fuel assemblies must be periodically replaced in order to maintain a sufficient level of core reactivity so that the nuclear fission process can be self-supporting. Refueling usually represents the largest time period during which the reactor is not producing power, and therefore every effort is made to minimize the refueling time.
The refueling operation includes removal from the reactor of internal structures such as the upper guide structure, and possibly control rods, so that the fuel assemblies are accessible for easy removal or rearrangement. Refueling is particularly time-consuming in those reactors which utilize the kind of upper guide structure described in U.S. Pat. No. 3,849,257. In such reactors, both the upper guide structure (UGS) and the control rods must be removed from the reactor before access can be had to the fuel assemblies. Previously, the control rods were individually removed from the reactor and hung in a temporary storage area. Then an overhead crane would lift the UGS and place it on a support platform.
It can be appreciated that the removal of individual control rods, the removal of the UGS, the reinsertion of the UGS, and the reinsertion of the individual control rods require many manual operations, during which several persons are exposed to radiation from the reactor core.